The present invention relates to a retractor (a winding device) for use in a seat belt device, particularly, to an improved retractor with a clamping mechanism which holds the webbing directly in an emergency of a vehicle to minimize the amount of draw-out of the webbing.
Conventionally, there has been employed a seat belt device which restrains an occupant of a vehicle to thereby protect the occupant against shocks given in a vehicle collision. The seat belt device employs a retractor of a type which includes not only an emergency locking mechanism for locking the rotation of a winding shaft with the webbing wound therearound in the draw-out direction thereof in a vehicle emergency such as a collision or the like, but also a clamping mechanism for holding the webbing directly to prevent the seat belt from being drawn out, thereby improving the restricting performance of the occupant in the early stage of the collision.
For example, a conventional clamping mechanism shown in FIG. 15 includes a wedge-shaped clamp 6 for clamping and engaging a webbing 26 between itself and a lower plate 16 fixed to a base back plate 1b of a retractor base 1 formed by bending a steel plate into a substantially U-shaped shape. The conventional clamping mechanism further includes an upper plate 20 having a sliding contact surface 20a capable of sliding contact with a plane portion 6d located opposite to a webbing opposing surface 6c of the clamp 6 for guiding the clamp 6 to a clamping and engaging position, whereby in a vehicle emergency a clamp lever 7 is operated to move the clamp 6 to the webbing clamping and engaging position, and the clamp 6 is wedged into an area between a sliding contact surface 20a of the upper plate 20 and the lower plate 16 to thereby hold the webbing 26.
And, in the webbing opposing surface 6c of the clamp 6, there are formed a plurality of substantially conical-shaped clamp teeth 6e in such a manner that they extend almost over the whole of the webbing surface opposed to the webbing opposing surface 6c. When the clamp 6 holds the webbing 26, the clamp teeth 6e bite into the surface of the webbing 26 to thereby prevent the webbing 26 from being drawn out from the retractor.
However, while the webbing 26 is being held by the clamp 6 and lower plate 16, if a strong tensile force is applied to the webbing to pull it out from the retractor, then not only a frictional force acting on the holding portion of the webbing 6 in the opposite direction to the webbing draw-out direction but also a thrusting force acting on the lower plate 16 are both increased, so that the clamp 6 is pressed against the lower plate 16 more strongly.
Then, as shown in FIG. 16 which is a horizontal section view of the main portions of the conventional clamping mechanism, both of the lower plate 16 and the base back plate 1b of the retractor base 1 are bent outwardly in the respective central portions thereof. As a result of this, the clamp teeth 6e formed on the two end portions of the clamp 6 in the webbing width direction thereof are thrust against the lower plate 16, so that the clamp 6 is not able to wedge between the sliding contact surface 20a of the upper plate 20 and the lower plate 16 sufficiently and thus the clamp teeth 6e formed on the central portion in the webbing width direction are not able to bite into the webbing 26 sufficiently.
Therefore, the biting force of the clamp teeth 6e formed on the clamp 6 into the webbing 26 is lowered as a whole, which makes it impossible to enhance the clamp force to hold the webbing 26 sufficiently. As a countermeasure against this, that the thickness of the lower plate 16 can be increased to enhance the rigidity thereof in order to prevent the lower plate 16 from bending. However, this increases not only the size of the lower plate 16 but also the weight thereof, which in turn increases the size of the retractor as a whole.